There are many ways to probe physical aspects of such microstate geometries.
The simplest and most interesting way to probe the microstate geometries may be studying geodesic motion of massive and massless particles in such spacetimes.
In particular it is an interesting issue what is significantly different between the motion of particles (e.g. the existence/nonexistence of stable bound orbits) in microstate geometries and that in black hole spacetimes.
Many researchers have so far studied particle motions in black hole spacetimes.
For example, it is well-known that in a four-dimensional Schwarzschild background, stable bound orbits exist for massive particles and do not exist for massless particles, whereas
in a five-dimensional Schwarzschild background, they do not exist for both massive and massless particles.
Moreover, stable bound orbits for rotating spherical black holes [1]}, [2]}, [3]}, [4]}, black holes with non-trivial topologies [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]} and Kaluza-Klein black holes [12]}, [13]} were also investigated.
On the other hand,
in supersymmetric microstate geometries [14]}, [15]}, massless particles with zero energy are stably trapped on an evanescent ergosurface, which are defined as timelike hypersurfaces such that a stationary Killing vector field becomes null there and timelike everywhere except there.
